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Piling: Breath of fresh air

Belfast’s newest port development will be the UK’s first bespoke harbour development for the offshore wind farm market. NCE reports.

Belfast Harbour may have been celebrating the 100th anniversary of the launch of the Titanic this year, but the port is hoping its latest development will have a longer term future than the ill-fated ship. Work currently underway to develop a 20ha area of the harbour specifically to serve the offshore wind farm construction market is the largest project in the harbour’s 400 year history - and it is a landmark scheme for more than just Belfast.

The new £50M facility will be the UK’s first bespoke offshore wind farm installation and preassembly harbour and the facility will initially serve as the base for development of the West of Duddon Sands wind farm off the coast of Cumbria. The project is being funded by Belfast Harbour itself but the facility will be leased to Dong Energy on completion in 2013 and with opening less than a year away, the site is a hive of activity.

“As well as speed, quality of installation, accurate pile positioning and alignment control were essential”

Belfast Harbour let the contract for construction of the port, which includes a new 480m long quay wall and deep water berth, to Farrans Construction.

The quay wall was constructed using the combi-wall method with 1,620mm diameter, 32m long tubes installed between 22m long PU22 sheet piles that were tied back to an anchor beam supported on 367, 30m long 660mm and 762mm diameter raked steel tubes.

Minimising settlement

The 17,000m2 quay slab also called for piled support to minimise settlement and Farrans installed 780, 750mm diameter CFA piles for the slab.

The work also included dredging the new berth and approaches. This involved the disposal of 500,000m3 of material to sea with treatment and disposal of some contaminated material to land. Behind the new quay slab itself, there is almost 20ha of heavy duty unbound pavement that will be used for the lay down and preassembly of wind turbine parts. Macaferri has supplied over 900,000m2 of geotextile, which will be used with almost 1M.t of aggregates to form the heavy duty pavement in this area.

The project was programmed at 60 weeks, but some of the major driven piling works had to be completed in just 11 weeks to clear the way for Farrans to work on other elements of the scheme. As well as speed, quality of installation, accurate pile positioning and alignment control were essential.

Farrans worked with ABI Equipment to develop a solution for the site. ABI proposed the use of two crane-suspended Delmag D100-13 diesel hammers mounted in rope-suspended lead systems for the impact driving of the combi-wall tubes.

“We liked the look of the simple, robust design of the Delmag diesel hammers and our project required us to select equipment with proven reliability if we were to meet the tight programme,” says Farrans site agent Tony Mulholland.

“We could also see operational benefits from using large impact hammers that did not require the use of separate hydraulic power packs and associated, cumbersome hose bundles.”
ABI also suggested using a purpose built piling rig for the rapid handling and installation of the raking anchor beam piles. “Our programme called for the tubular raking piles to be accurately installed in an exceptionally tight time frame,” says Mulholland.

“We needed to implement a mechanised approach and the rig enabled us to comfortably achieve our deadline with excellent installation quality.”

The raking piling rig was equipped with a Delmag D46 hammer set-up to drive the 660mm and 762mm diameter piles at 1 in 3 from vertical.

“We had hoped to achieve around six piles per day but we were easily able to exceed this,” adds Mullholland. “The overall performance of the system meant we were able to make up time when bad weather hit us.”

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